Optimization of Phase Purity of β′‐Sialon Ceramics Produced from Silazanes and Nano‐Sized Alumina

Abstract

The use of preceramic polymers in the synthesis of Sialon ceramics has been scarcely discussed in the literature. In this article we report the production of virtually phase-pure β′-Sialon ceramics from a mixture of commercially available polysilazanes and γ-Al2O3 nanopowder, pyrolized in N2 atmosphere in the 1300°C–1600°C range. This approach combines the advantage of embedding nano-sized fillers in preceramic polymers, in terms of their reactivity towards the Si–N based ceramic pyrolysis residue, with the complex interactions with residual carbon, also present as a secondary phase in the same ceramic residue. Starting from a polymer (PSZ20) yielding a SiCN amorphous ceramic after pyrolysis, the Sialon phase purity is greatly affected by the residual C content: for an optimized polymer/filler ratio (PSZ20/Al2O3 = 2), β′-Sialon can be produced possesing only small quantities of quasi-amorphous SiC as a secondary phase. Additional improvements based on the partial replacement of PSZ20 with a polymer (PHPS) not containing C in the backbone, lead to the production of pure nanocrystalline β′-Sialon powders (average grain size of 100–200 nm)

Preceramic Polymer‐Derived SiAlON as Sintering Aid for Silicon Nitride

“…1, hot pressing of both sintering aid precursor powders (see heat-treatment conditions in Table II, samples PA and PB) resulted in a different phase compositions. 8,17 The diffraction patterns of hot-pressed Si 3 N 4 powders mixed with 18 wt% powder A and powder B (from now on referred to as "series A" and "series B") are shown in Figs. Contrary to our previous results, 21 b-SiAlON was totally absent in both samples.…”

“…1 The introduction of fillers of different nature is a suitable way to limit these drawbacks and allows the realization of relatively large components with reduced or even absent shrinkage and limited residual porosity. [7][8][9][10] The unique microstructure of PDCs, based on the nanosized domains and leading to high chemical durability and high creep resistance, could also be exploited for the realization of high-performance intergranular phases for advanced ceramics, such as SiC and Si 3 N 4 . 6 This approach was successfully applied to the synthesis of oxynitride ceramics (SiAlONs), showing interesting mechanical and functional properties.…”

Multifunctional advanced ceramics from preceramic polymers and nano-sized active fillers

“…In fact, we had to adjust the formulation iteratively, after evaluation of the diffraction patterns for the processed material, taking into account several side reactions and secondary phenomena (such as carbothermal reduction reactions, volatilization of Si-containing components, nitrogen diffusion from the firing atmosphere into the component) whose occurrence contributes to modifying the composition (and therefore phase assemblage) of the resulting ceramic. 62 In the end, however, it was possible to produce pure ␤ -SiAlON (Si 6−z Al z O z N 8−z , with z = 2.9) starting from an optimized mixture of silazanes and ␥-Al 2 O 3 nanoparticles, 62 as shown in Fig. 2d.…”

“…The oxygen content in the final ceramic product, as an example, is higher than expected, leading to the O -phase as an intermediate phase (1300 • C), before nucleation of ␤ -SiAlON (at temperature ≥1400 • C). 62 An enhanced polymer-alumina ratio (the upper pattern of Fig. 3b represents the result of the formulation of Eq.…”

“…The powders were then subjected to shaping using several methods, including cold uniaxial pressing (pressure of 20-40 MPa), warm pressing (180 • C, 20 MPa), extrusion, injection molding, foaming, fused deposition, indirect 3D printing, machining and coating (after dispersing in water or when still in the dissolved state). Details for the specific [62] n.a. : not available.…”